1. Field of the Invention
The present invention relates to a method of manufacturing a dynamic amount semiconductor sensor having a beam structure for detecting a dynamic amount of such as acceleration, yaw rate, or vibration.
2. Related Arts
The inventors of the present invention proposes, as a dynamic amount semiconductor sensor, a servo-control and differential capacitance type acceleration sensor using an SOI (Silicon-On-Insulator) substrate in JP-A-9-211022. JP-A-9-211011 was not opened and not printed when the present invention was made by the inventors. The method of manufacturing the acceleration sensor includes a process in which a polycrystalline silicon (poly-silicon) layer (bonding layer) formed on a first substrate is bonded to a second substrate (bonding substrate) after the first substrate is flattened. As a result of examinations and studies, the inventors of the present invention found a problem in the process that the poly-silicon layer cannot be sufficiently flattened, so that this may adversely affect the bonding property between the bonding substrate and the poly-silicon layer. When the thickness of the poly-silicon layer is increased, the above problem may be solved. However, in this case, the time for forming the poly-silicon layer is considerably lengthened, resulting in increase in manufacturing cost.
In addition, when the acceleration sensor is manufactured, first of all, grooves are formed in the first substrate, and then the grooves are filled with a silicon oxide layer when the silicon oxide layer is deposited on the first substrate. After the first and second substrates are bonded to each other through the poly-silicon layer, finally, the silicon oxide layer embedded in the grooves is removed by an etching process or the like. As a result, fixed electrodes and a movable beam structure composed of a mass part, movable electrodes, and beams are provided. However, in this method, to fill the grooves with the silicon oxide layer, it is necessary that each width of the grooves is twice larger than the thickness of the silicon oxide layer at most. The limit to the widths of the grooves results in limits to structural parameters of the acceleration sensor such as gaps between the movable electrodes and the fixed electrodes and the widths of the beams. This problem occurs in other dynamic amount sensors such as a yaw rate sensor as well.